Conventional types of control circuit for vibrating compressors are such that the d-c voltage of a battery, etc. is converted into an a-c voltage, which is applied to the vibrating compressor. In converting a d-c voltage into an a-c voltage, an a-c voltage of a frequency agreeing with the mechanical vibration of the vibrating compressor is generated and applied to the vibrating compressor.
Conventional types of control circuit for vibrating compressors have heretofore used a circuit configuration in which a switching element, such as a MOS-FET transistor, converts the d-c voltage of a battery into an a-c voltage, which is in turn applied directly to the vibrating compressor.
For this reason, the battery voltage during or immediately after the charging of the battery is normally higher than the predetermined voltage, and accordingly the converted a-c voltage of a frequency agreeing with the mechanical vibration of the vibrating compressor also tends to be higher, causing or threatening to cause a damage to the valve due to the overrun of the vibrating compressor piston.
If the ambient temperature of the vibrating compressor drops, the delivery pressure of the vibrating compressor also drops, causing the stroke of the vibrating compressor piston to increase. As a result, when the ambient temperature of the vibrating compressor is lower than a predetermined temperature, a damage is caused or threatens to be caused to the valve due to the overrun of the vibrating compressor piston even when a predetermined voltage is applied to the vibrating compressor.